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Photons and transparency...who's right?

  1. Jun 3, 2015 #1
    All, I have read as much as I can find online regarding this topic and there are so many conflicting answers that it is insane.

    First, many sources identify photons vibrating the electrons in a transparent material in such a way that the net effect is to pass the photons out the other end of the medium. In this case, it seems to me that photons are being absorbed and re-emitted by each electron on the way through. HOWEVER, other sources state that photons pass through the medium (such as glass) and are not affected because they do not have sufficient energy to be "absorbed" by the electron...in other words...no interaction occurs.

    1. But, is it not correct to say that anytime a photon interacts with an electron that it DOES absorb the energy, but perhaps not enough to jump energy levels?

    2. In the case of reflection, the electron would absorb enough energy to jump to a higher state, and then re-emit the photon again as light. Therefore, reflection also requires an absorption of energy first, too. Correct?

    Thanks in advance.
  2. jcsd
  3. Jun 3, 2015 #2
    It is horribly complicated to describe light in materials using photons. To do it right would require to treat the whole system in QED - quantum electrodynamics. If you want to understand what is going, a classical picture with electromagnetic waves and Lorentz oscillators is much more accessible.
  4. Jun 3, 2015 #3
    So, is there even necessarily a correct mental model to have regarding the behavior of photons in a transparent medium?
  5. Jun 3, 2015 #4
    Perhaps a more specific question. Is it correct to say that any time a photon interacts with an electron, it is absorbed? Or, can you ever think of a photon reflecting from an electron as billiard balls would?
  6. Jun 3, 2015 #5
    A transparent medium like glass contains electrons that are bound more strongly than the photon energy. So you cannot describe this with just the interaction between a photon and a free electron. Only for free electrons you could do that: the Compton effect, conservation of energy and momentum, like billiard balls.
  7. Jun 3, 2015 #6


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    Please start with our FAQ

    https://www.physicsforums.com/threads/do-photons-move-slower-in-a-solid-medium.511177/ [Broken]

    Last edited by a moderator: May 7, 2017
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